Seasonal timing adaptation across the geographic range of Arabidopsis thaliana

Moises Exposito-Alonso - PNAS May 5, 2020 117 (18) 9665-9667

Figure: Distribution of seasonal timing adaptation of A. thaliana. (A) Map of predictions of plant’s time to flowering and senescence, temperature-independent germination rate, and cold-induced/blocked spring germination projected in a red–green–blue space. Black crosses indicate the locations of four ecotypes. (B and C) Relationships between the three variables centered on their averages. The gray dotted line indicates 290 d to senescence, which approximately coincides with the strict requirement of vernalization to flower (8). (D) Months with minimum temperature below 0 °C and monthly precipitation for the four locations in A of representative natural ecotypes: Tri-0 from south Spain (1001 Genomes Project identification code: 9900), Fun-0 from central Spain (1001 Genomes Project identification code: 9542), Hi-4 from Germany (1001 Genomes Project identification code: 9782), and Dör-10 from Sweden (1001 Genomes Project identification code: 5856). Grayscale maps are at https://doi.org/10.6084/m9.figshare.11724039.

The most fundamental genetic program of an annual plant defines when to grow and reproduce and when to remain dormant in the soil as a seed. With the right timing, plants can even live in hostile regions with only a few months of growth-favorable abundant rains and mild temperatures. To achieve this, plants have evolved molecular pathways that sense environmental variables and trigger their two main lifecycle transitions: germination and flowering. Growing season length—which depends on photoperiod, temperature, and rainfall patterns—drastically changes even over short geographic distances, and therefore, it is common that populations of the same species vary genetically to adjust to the local seasons. The widespread annual plant Arabidopsis thaliana has been a key model to study these seasonal timing adaptations and dissect their genetic components. Previous work on seasonal adaptation heavily focused on temperature-dependent flowering time pathways, including the cold-sensing genes FRIGIDA (FRI) and FLOWERING LOCUS C (FLC). This knowledge pointed at two main strategies: winter and spring annual plants. A new study in PNAS from Martínez-Berdeja et al. (1) comprehensively documents germination timing across the geographic distribution of A. thaliana and supports the gene DELAY OF GERMINATION 1 (DOG1) as one key genetic determinant of seasonal timing adaptation. Using their data, here I visualize the complex interactions of flowering and germination time and local climates across A. thaliana’s native geographic range and synthesize its seasonal timing adaptation into four categories:

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Mediterranean rapid cyclers, facultative winter cyclers, weedy summer/spring cyclers, and strict Scandinavian winter cyclers.

With climates across the world changing in annual averages as well as seasonal patterns (20), a deep understanding on seasonal timing adaptation becomes of crucial importance to foresee impacts of climate change on species. Large-scale datasets that study seasonal timing traits and their genetic basis in a species, such as the one produced by Martínez-Berdeja et al. (1), will be instrumental to develop realistic models that integrate ecological, demographic, and evolutionary processes to anticipate species’ (mal-)adaptive responses to climate change.

See https://www.pnas.org/content/117/18/9665